1. Field of the Invention
The present invention relates to a technique that determines the amount of impurities present in the vicinity of an insulating film formed on surface of a substrate.
2. Description of the Related Art
An insulating film formed on a surface of a substrate, such as a semiconductor wafer, is often contaminated with mobile ions including alkali metal ions (hereinafter referred to as `intra-film impurity ions`) in the course of wafer processing. These intra-film impurity ions readily move under the influence of an electric field and thereby lower the stability of electric characteristics of the surface of the semiconductor wafer.
The amount of intra-film impurity ions in the insulating film is generally measured by C-V characteristic measurement with the aid of BT (bias temperature) treatment. In the BT treatment, a direct current bias is applied to a gate electrode on the insulating film at high temperatures.
The BT treatment heats up the semiconductor wafer to high temperatures and thereby requires a relatively long treatment time.